1. Field of the Invention
This invention relates to pressure sensitive adhesives (PSA) used in wallcoverings, borders, appliques and the like, and more specifically, to a PSA containing hollow glass bubbles allowing wallcovering to be both removable and repositionable.
2. Related Art
Wallcovering products have traditionally been attached to a wall surface using aqueous starch or cellulosic based pastes. The paste composition is brushed onto the surface of the wallcovering immediately before applying to the wall surface. For prepasted wallcovering, the adhesive is coated and dried on the wallcovering surface during manufacture. Prior to hanging, the paste is activated by soaking the wallcovering sheets in water. These traditional types of wallcovering paste have many inherent disadvantages. When paste is brushed on a wallcovering surface, there is a wide variation in the amount applied. The process of applying paste and soaking of prepasted wallcovering is time consuming and very messy. The resultant wallcoverings are also initially very wet and can be easily distorted and even torn during application to a wall surface and during trimming. Once applied to a wall, wet wallcoverings shrink as they dry causing seam separation and lifting. Therefore, an improved adhesive composition is desirable for attaching wallcovering products to a wall surface.
The prior art describes attempts to overcome the deficiencies of traditional paste adhesives. For example, Erwin, U.S. Pat. No. 3,314,838, describes a pressure sensitive adhesive composition containing hollow glass microspheres which is first applied to the wall surface and dried. A decorative film such as a wallcovering applied to the surface of the adhesive composition on the wall can be easily slid into position. A permanent bond is obtained by application of pressure which crushes the microspheres. However, Erwin does not address the problem of variation in the amount of adhesive composition on the wall resulting from hand application. Considerable time is also required to apply and dry the adhesive composition on the wall. Further, the adhesive composition of Erwin is permanent since removal from the wall results in damage to the wallpaper or the wall surface.
Danielson and Berg, U.S. Pat. No. 3,331,729, describe a pressure sensitive sheet material and method of application whereby the sets are easily repositioned during application to a floor surface. In manufacture of this product, hollow microspheres are electrostatically applied to a web of thermoplastic polymer coated paper. This thermoplastic polymer is primarily polyethylene which can be easily softened with heat and allow the glass microspheres to penetrate up to one half of their diameter into the softened film. A pressure sensitive adhesive composition is then coated on the polymer film with embedded microspheres. A decorative film is then laminated to the adhesive surface to form the final construction. To apply the decorative film to a surface like a floor, the polyethylene film is first stripped from the product to expose the adhesive surface covered with protruding microspheres. The resultant product is easily slid into position and then pressure is applied to crush or distort the microspheres to bring the floor and adhesive into contact. This prior art, however, has several disadvantages. The process of softening the polyethylene film to embed the hollow microspheres is difficult to control. The process is also limited to thermoplastic films with relatively low softening points like polyethylene. Further, the disclosed adhesives are strong and thus, for example, do not allow removal from a wall surface without causing damage.
Morgan, U.S. Pat. No. 3,554,835, describes a slidable adhesive laminate which has spaced dots of release material on the surface. Special processing methods are needed to produce this laminate. The release material also remains and contaminates the product and affects adhesion properties.
Fischer and Whalen, U.S. Pat. No. 3,663,269, describe wallcovering having an encapsulated adhesive layer which is repositionable before heat and pressure is applied. The process to make encapsulated products is involved and very expensive. The adhesive is heat activatable at 190.degree. to 200.degree. F. To uniformly apply heat while installing wallcovering would also be difficult and time consuming.
Reed and Stafford in U.S. Pat. No. 4,054,697 describe PSA coated decorative sheet materials which can be slid on a substrate surface. The PSA layer is covered with particles of urethane foam which is deformed under pressure to expose the adhesive and form a bond with a wall, floor or countertop. The PSA for the application needs to be strong to keep the foam particles from recovering. Curable adhesive compositions are desirable for this. Such adhesives would be expected to form a permanent bond with the substrate and not be removable.
Parrotta, U.S. Pat. No. 4,376,151, describes a business form that has a PSA which is covered with microspheres. Application of pressure displaces the microspheres and exposes the tacky adhesive. The adhesive is first coated on the substrate and the microspheres are coated on top of the adhesive. Alternatively, low density microspheres are mixed with the adhesive, and after coating on a substrate, they float to the surface of the adhesive. The adhesive for the resultant business form is described as permanent and cannot be removed without tearing the substrate.
Calhoun and Koskenmaki, U.S. Pat. No. 5,141,790, describe a repositionable adhesive tape that has spaced clumps of glass bead particles distributed over the surface of the PSA. The process to produce this product is difficult because the clumps are made by filling depressions either in a carrier web or in a rotating transfer drum.
Wilson, Meixner, Bemis, Calhoun and Ree, U.S. Pat. No. 5,362,516, describe a method of making a repositionable adhesive sheet which has a microstructure surface comprising a plurality of adhesive pegs which can contain beads. Firm bonds are obtained by compressing the pegs to increase contact area. Special processing methods are also required to place regularly spaced adhesive pegs on the sheet surface.
DeProspero, Banas, Muny and Frye, U.S. Pat. No. 5,639,539 describe a releasable wallcovering which uses a pressure sensitive adhesive layer formed of tacky polymeric microspheres. However, a wallcovering product using this type of adhesive could not be easily slid on a wall surface for repositioning. To reposition such a wallcovering, the wallcovering must be removed from the wall and reapplied in a new position. Therefore, working with this type of wallcovering requires extra skill and time, and increases the likelihood of tearing the wallcovering.
Rusincovitch and Roe, EP 0609603A1, disclose a repositionable wallcovering in which the adhesive layer is covered with a web or net which limits contact with a wall until pressure is applied. These inventors also disclose in U.S. Pat. No. 5,487,929 a decorative sheet material which has a pattern coated adhesive with non adhesive projections. It was important to have an adhesive pattern with specific size and shape. The products described in these inventions require extra manufacturing steps and related costs.
Gibson, GB Patent 2,117,271, describes a wallcovering adhesive which is foamed to limit initial contact with the wall. Pressure collapses the foamed adhesive to form the bond. The adhesive surface also must have a high energy heat treatment to provide a porous non tacky surface.
All of the prior art mentioned above have limitations. In many cases, the need for both repositionability and removability is not addressed. In other cases, special manufacturing methods are required which cause product variability and add cost.
Therefore, there is a need for an adhesive layer for wallcover that uses a pressure sensitive adhesive, resulting in the wallcovering having both removable and repositionable properties.